Start the game and click the tools button on the lower
right of the screen. Select "load" in the menu that follows. From there you can select which campaign you want and select the mission. Then, once it loads, click Tools, Play Mission and you can play it. Doing this you can even see the cinimatics and how they make them too.

Hints:
Never underestimate the power of artillery in deciding
a battle. With proper spotter support, artillery can
wreak havoc on an enemy base in little time.

Build a variety of defenses to guard against both ground
and air attacks. Nothing ruins your day like watching
a sole air unit destroy a building by itself because
you've got nothing that can shoot it down.

Always explore the map as quickly as possible, locate where
the resources and strategic choke points are, and then
defend them. Don't let the enemy build up momentum.